Syudy material of bayesian IRF and posterior shock decomposi

Dear all:
I use dynare to finish my thesis(master student) and will have a thesis defending next month.Because you know that dynare do everything for you and I only know how it does bayesian parameter estimation upon “Dynare user guide” but I don’t know theory of how it get bayesian IRF and posterior shock decomposion. can anybody give me some study material of bayesian IRF and posterior shock decomposion since I am afraid the commit members will ask such quesitions ? Thank you all!